1. Field of the Invention
This invention relates to edge-emitting semiconductor lasers that are manufactured on a single fabrication wafer and, more specifically, to an edge-emitting semiconductor laser that is capable of being optically tested while it is still located on the fabrication wafer (prior to cleaving or sawing).
2. Background of the Related Art
Edge-emitting lasers are semiconductor lasers with horizontal laser cavities (resonant cavities that are parallel to the plane of the wafer on which they are fabricated) that emit outputs in a horizontal direction through the edges of the laser. When manufacturing edge-emitting lasers, multiple laser cavities are usually formed in parallel strips on the surface of a single fabrication wafer. Each strip is divided into multiple segments to form multiple coaxial lasers on the wafer. The fabrication wafer is then cleaved or sawed to separate the individual lasers.
As many as 25,000 or more individual lasers can generally be fabricated on a single fabrication wafer. Each individual laser is typically tested for quality control purposes. This generally involves measuring the laser emission as a function of applied current. xe2x80x9cOn-waferxe2x80x9d testing, in which each laser is tested while they are still on the fabrication wafer, is the most efficient and cost effective way of testing the lasers.
However, because edge-emitting lasers emit light from their respective edges, the light emitted from most of the lasers (except the lasers at the very edge of the fabrication wafer) get blocked by other adjacent lasers, and thus is not detectable. Thus, edge-emitting lasers must be tested after they have been separated by cleaving or sawing the fabrication wafer. This is very time consuming, and thus increases manufacturing costs significantly.
Vertical cavity surface-emitting lasers were developed, in part, because on-wafer testing is so desirable in terms of efficiency and cost reduction. Vertical cavity surface-emitting lasers have resonant cavities that are perpendicular to the plane of the fabrication wafer, and thus emit light vertically with respect to the fabrication wafer. The vertically-emitted light from each laser can be measured prior to cleaving or sawing of the fabrication wafer, because the light is not blocked by adjacent lasers.
However, vertical resonant cavities are difficult to fabricate and require complicated device processing techniques. Further, vertical cavity surface-emitting lasers have lower output powers and quantum efficiencies than edge-emitting lasers.
The above references are incorporated by reference herein where appropriate for appropriate teachings of additional or alternative details, features and/or technical background.
An object of the invention is to solve at least the above problems and/or disadvantages discussed above and to provide at least the advantages described hereinafter.
The present invention provides a system and method of testing multiple edge-emitting lasers on a common fabrication wafer. This is accomplished by providing, for each edge-emitting laser on a common fabrication wafer, a structure that re-directs a portion of the edge-emitted light from each edge-emitting laser in a direction such that the re-directed portion from each edge-emitting laser can be measured while the edge-emitting lasers are still on the fabrication wafer. Each edge-emitting laser on the wafer can therefore be easily tested without cleaving or breaking the wafer into multiple pieces.
The present invention may be practiced in whole or in part by an edge-emitting laser, comprising a resonant cavity and a second order or higher grating formed in the resonator, wherein the second order or higher grating transmits a first portion of light in the resonator along a first direction as edge-emitted light, and directs a second portion of light in the resonator along a different direction.
The present invention may also be practiced in whole or in part by a horizontal cavity edge emitting laser comprising a resonant cavity and a trench positioned proximate to the resonant cavity that is configured to scatter a portion of light in the resonant cavity such that the scattered portion can be measured.
The present invention may also be practiced in whole or in part by a method of testing at least two horizontal cavity edge-emitting lasers on a common wafer, comprising re-directing a portion of the light generated by each edge-emitting laser such that the re-directed portion can be detected while the edge-emitting lasers reside on the common wafer.
Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention. The objects and advantages of the invention may be realized and attained as particularly pointed out in the appended claims.